As is known in the art, it is common to provide a liquid in a vessel that is utilized, e.g., in a commercial process of one type or another. The vessel may suitably serve as a source of supply for the liquid in which case it will be important in many instances to maintain a desired level of the liquid within the vessel. By way of example, a printing press is known to require a source of ink that must be continuously replenished in the course of a printing operation.
Most commonly, control systems for maintaining the level of liquid in a vessel have utilized a float element that is supported on the surface of the liquid. This type of control system depends upon the float element riding up and down as the level of the liquid fluctuates within the vessel to activate respective off and on switches to control suitable valves for selectively replenishing the liquid from a remote source. More specifically, the actuation of the switches that control the valves is typically accomplished either mechanically or by energizing a proximity sensing device.
Generally speaking, such control systems are well proven and quite reliable for most applications. However, they are known to be unsuitable for use in an ink environment. Basically, this is due to the fact that ink has a high viscosity and tack which causes it to adhere to the float element.
Because of these characteristics of ink, the buoyancy and weight of the float element in this type of control system is known to change dramatically. As a result of these changes in buoyancy and weight, the control system is known to be difficult, at best, to maintain in calibration within an ink environment.
As an alternative to float-type control systems, it is also generally known that ultrasound instruments have been utilized to control the level of liquid in a vessel. The ultrasound instruments function by detecting an acoustic wave which is reflected from a surface of the liquid in the vessel and by measuring the time which elapses between the emission and detection of the wave to thereby calculate the distance of the liquid surface from the instrument. Unfortunately, the ultrasound instruments are quite unreliable in an ink environment inasmuch as the ink surface is quite irregular preventing a proper reflection of the acoustic wave.
The present invention is directed to overcoiming one or more of the foregoing problems and achieving one or more of the resulting objects.